At-the-bench reference. For why the math works the way it does, see Reconstitution Fundamentals; for the syringe and unit-mark mechanics, see Syringe, Draw and Dosage Math.
The core formula
Concentration (mcg/unit) = Total mcg in vial ÷ Total units of BAC water added.
An insulin syringe is graduated in units, where 100 units = 1 mL on a U-100 syringe. So a vial reconstituted with 1 mL of BAC water has 100 units of solution inside, regardless of vial peptide content.
Common cases
| Vial | BAC water | Concentration | For 100 mcg dose | For 250 mcg dose | For 500 mcg dose | For 1 mg dose |
|---|---|---|---|---|---|---|
| 2 mg | 1 mL (100 u) | 20 mcg/unit | 5 u | 12.5 u | 25 u | 50 u |
| 2 mg | 2 mL (200 u) | 10 mcg/unit | 10 u | 25 u | 50 u | 100 u (1 mL) |
| 5 mg | 1 mL (100 u) | 50 mcg/unit | 2 u | 5 u | 10 u | 20 u |
| 5 mg | 2 mL (200 u) | 25 mcg/unit | 4 u | 10 u | 20 u | 40 u |
| 5 mg | 2.5 mL (250 u) | 20 mcg/unit | 5 u | 12.5 u | 25 u | 50 u |
| 10 mg | 2 mL (200 u) | 50 mcg/unit | 2 u | 5 u | 10 u | 20 u |
| 10 mg | 3 mL (300 u) | ~33.3 mcg/unit | 3 u | ~7.5 u | 15 u | 30 u |
| 10 mg | 5 mL (500 u) | 20 mcg/unit | 5 u | 12.5 u | 25 u | 50 u |
Picking the BAC volume
- Want round-number unit marks? Pick a BAC volume that makes your typical dose land on whole units. For a 250 mcg dose from a 5 mg vial, 2 mL gives you 10 u (clean). For a 100 mcg dose from a 2 mg vial, 2 mL gives you 10 u (clean).
- Want minimum waste? Lower BAC volume = higher concentration = smaller draw volume = less peptide left in the syringe dead space and on the needle.
- Want longer fridge life? Higher BAC volume dilutes the BA concentration too. Most reconstituted peptides are good for 28–30 days refrigerated regardless; if you're running >2 mL of BAC water on a single vial, factor in the BA dilution.
Common mistakes
- Confusing units with mL. 10 u on a U-100 insulin syringe is 0.1 mL. 50 u is 0.5 mL. Read the unit mark, not the imagined mL.
- Half-unit doses on a U-100 syringe. Most U-100 insulin syringes don't graduate finer than whole units. If your math lands on 12.5 u, either pick a BAC volume that produces whole-unit marks for your dose, or accept the 0.5-unit error.
- Counting from the wrong end. The plunger’s leading edge against the unit mark is what counts, not the trailing edge of the rubber stopper. Eye level on a flat surface, not at an angle.
- Forgetting to invert and tap. BA water added too forcefully onto lyophilised powder can cause foam and protein damage. Stream the BA water down the vial wall, then gently invert - do not shake.
Cross-references
- Reconstitution Fundamentals - the underlying mechanics, BAC water selection, and stability rules.
- Syringe, Draw and Dosage Math - gauge selection, dead space, and the wider-volume math.
- Blend Ratio Dosing - for multi-peptide blends where the per-component concentration matters.
- Storage and Handling Best Practices - cold-chain rules for the reconstituted vial.